The present invention relates to an image forming apparatus.
In a conventional image forming apparatus such as a printer, a copier, a facsimile, and the likes, image forming units are provided for forming images in yellow, magenta, cyan, and black. In each of the image forming units, a charge roller uniformly charges a surface of a photosensitive drum, and an LED (Light Emitting Diode) head exposes the surface of the photosensitive drum to form a static latent image thereon. Then, a developing roller develops the static latent image, thereby forming a toner image in each color. A transfer roller transfers and overlaps the toner images to a sheet, thereby forming a color toner image. A fixing device fixes the color toner image to the sheet, thereby forming a color image on the sheet.
In general, when toner of each color, i.e., yellow, magenta, cyan, and black, contains a large amount of wax, it is possible to form an image with high gloss. Accordingly, when a photograph is printed in colors, toner of each color containing a large amount of wax is used, thereby making it possible to form a color image having image quality similar to that of the photograph as much as possible. Note that when a photograph is printed in monochrome, it is tried to form a monochrome image having image quality similar to that of the photograph as much as possible.
On the other hand, when a text or a graph is printed, it is preferred to from an image with low gloss. To this end, a conventional printer may be provided with two types of image forming units. One of the image forming units uses black toner containing a small amount of wax, and the other one of the image forming units uses black toner containing a large amount of wax. The printer further includes a plurality of fixing devices having different transfer temperatures (refer to Patent Reference).    Patent Reference Japan Patent Publication No. 2002-372882
In the conventional printer, in order to form both an image with high gloss and an image with low gloss, it is necessary to provide a plurality of the image forming units and a plurality of the fixing devices, thereby making a transportation path of a sheet and a configuration of the printer complicated. Accordingly, it is difficult to cool the printer, thereby increasing a temperature inside the printer. As a result, there may occur problems such as hot offset or uneven fixing in the fixing devices, thereby deteriorating image quality.
In view of the problems described above, an object of the present invention is to provide an image forming apparatus capable of solving the problems of the conventional printer. In the image forming apparatus of the present invention, it is possible to form both an image with high gloss and an image with low gloss, and further to improve image quality.
Further objects of the invention will be apparent from the following description of the invention.